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Whakatane / Waimana Catchment

Geology and Geography of the CatchmentWhakatane harbour

The Whakatane River system meets the sea at Whakatane township, it broadly comprises two main branches; the Waimana River and the Whakatane River. The Waimana Catchment covers 440 km2 extending 77 km from Taneatua to its upper tributaries. Both catchments are relatively narrow and the tributaries are short and steep, draining extensive bush covered catchments.
The Waimana River valley floor is narrow and has few areas of river flats in the upper 48 km, but after leaving the main range the floor widens and for the next 19.5 km the river channel is wide and braided. The final 13 km of the Waimana River are through a gorge with the exception of the last 1.6 km where it empties out of the gorge on to the valley floor just upstream of the confluence with the Whakatane River at Taneatua.
The Whakatane River rises in the Huiarau Range and quickly drops into a deeply incised valley and there are no significant river flats for the next 64 km until the river flows out of the main range at the upper Ruatoki Valley. At this point the valley floor widens out to an average width of 1,600 metres before widening out again at the limeworks. Below this for the next 6.5 km the river has developed a wide meander belt with considerable areas of shingle bed and marginal river flats. Below the Ruatoki Bridge which is 26.6 km upstream of the sea, the river is generally more confined due to the establishment of willow edge protection until it reaches the confluence with the Waimana. From there it continues for another 3.5 km before it reaches the Pekatahi Bridge and below this the river is stop banked.Upper River
The main foothill streams are the Owhakatoro (74 km2), the Waiho (89 km2), Te Rahu (30 km2), Wainui Te Whara (6 km2) and Wairere (3 km2).
The areas of river flats (floodplains) around the two rivers are comprised of Taupō and Kaharoa Breccia and volcanic alluvium, while the majority of the hill country extending into the ranges is comprised of ashes older the Taupō Pumice. The underlying rock foundation over the whole of the area is greywacke.

Land Use in the Catchment

Land cover and usage affects run-off, which affects the magnitude of flooding. For example urban areas, which tend to have more impermeable surfaces typically increase runoff and flood risk. Heavily vegetated areas, such as forestry on the other hand tend to reduce run-off and lower the flood risk.

Rural

Land Use

Area (ha)

Productive ha

% Productive Land-use

Indigenous and exotic forest

153,698

 

 

Dairy farming

12,793

12,793

65.6%

Drystock farming

5,870

5,870

30.1%

Unproductive

2,160

 

 

Small holdings

2,015

 

 

Scrub

1,022

 

 

Cropping

842

842

4.3%

Total

178,400

19,505

 

Excluding Indigenous forest, the most common land-use is dairy farming, which represents 66% of the productive land area. Drystock farming and cropping represent 30% and 4% respectively.
The Whakatane-Waimana River catchment extends as far south as Ruatahuna, situated in the upper catchment 75km from the coast. The majority of productive land (98%) is situated in the lower Catchment within 25 kilometres of the Bay of Plenty coast.

Urban

Urban areas comprise residential, commercial and industrial uses. The settlements of Whakatane, Taneatua, and Waimana are the main urban areas within this catchment.

Flood Risk Management in the CatchmentWakatane Waimana stopbanks

The Whakatane River Scheme is a river and drainage scheme that includes; substantial stop banking of the main river and some major tributaries, floodgates, gravity and pumped drainage outlets, and considerable channel edge (bank) protection and plantings. The scheme includes the Whakatane and Waimana Rivers and the Te Rahu, Waioho and Wairere Tributaries.
The aim of the original scheme was to provide 100 year flood protection along the lower 12.8 km of river, partial flood protection and channel improvements along the upper 30.4 km of the Whakatane River and 28.8 km of the Waimana River, and improved drainage for approximately 4,000-6,000 hectares of the Eastern Rangitaiki Plains. Previous to the scheme extensive flooding was a common event for the low lying areas generally north of the Awakeri-Taneatua railway line, from western drain in the west to Waioho Stream and up the Whakatane River valley. Whakatane Borough was subject to flooding on the westernside, and was unable to be developed for housing until after the construction of the nearby stopbanks and channel control works. Scheme construction commenced in 1965 and was completed in 1981.

View map of Whakatane / Waimana stopbanks (pdf 5.3MB)

Link to more info on the Whakatane Waimana River control scheme 

Significant floods in the Catchment

There have been a number of significant floods in this catchment in the last hundred years. 
The township of Whakatane has two different types of rain events that cause flooding, this is due to the shape of the catchment and the land within it. The streams with short steep catchments in the hills around Whakatane can rise very quickly and cause significant flooding to urban catchments, overwhelming the stormwater systems and inundating homes, they can also carry mud and debris. This type of flooding occurs when alot of rain falls in a very short amount of time, we call this a high intensity short duration rain event. The flood in January 2011 was an example of this. During this type of event the main rivers might go into flood.
The other type of rainfall event that causes flooding in the Whakatane Waimana catchment is when there is a prolonged period of significantly heavy rain. This type of event will cause the rivers to rise and may cause them to flood. The flood events in 1965, 1998 and 2004 were examples of this type of flooding.